Is the enhancement of type II radio bursts during CME interactions related to the associated solar energetic particle event?

TL;DR

This study links enhanced type II radio bursts during CME interactions to larger SEP events, showing that specific CME properties and interaction dynamics significantly influence SEP intensities.

Contribution

It provides new evidence that CME interactions with certain characteristics are key to producing large SEP events, highlighting the role of type II radio burst enhancement as a discriminator.

Findings

Enhanced type II radio bursts are associated with large SEP events.

Main CMEs with higher speed, width, mass, and energy drive stronger shocks.

SEP intensities negatively correlate with CME intersection height.

Abstract

We investigated 64 pairs of interacting-CME events identified by the simultaneous observations of SOHO and STEREO spacecraft from 2010 January to 2014 August, to examine the relationship between the large SEP events in the energy of 25-60MeV and the properties of the interacting CMEs. We found that during CME interactions the large SEP events in this study were all generated by CMEs with the presence of enhanced type II radio bursts, which also have wider longitudinal distributions comparing to events with the absence of type II radio burst or its enhancement (almost associated with small SEP events). It seems that the signature of type II radio bursts enhancement is a good discriminator between large SEP and small or none SEP event producers during CME interactions. The type II radio burst enhancement is more likely to be generated by CME interactions, with the main CME having larger speed (v), angular width (WD), mass (m) and kinetic energy (E_k), that taking over the preceding CMEs which also have higher v, WD, m and E_k, than those preceding CMEs in CME pairs missing the type II radio bursts or enhancements. Our analysis also revealed that the intensities of associated SEP events correlate negatively with the intersection height of the two CMEs. Most of type-II-enhanced events and SEP events are coincidentally and almost always made by the fast and wide main CMEs that sweeping fully over a relatively slower and narrower preceding CMEs. We suggest that a fast CME with enough energy completely overtaking a relatively narrower preceding CME, especially in low height, can drive more energetic shock signified by the enhanced type II radio bursts. The shock may accelerate ambient particles and lead to large SEP event more easily.